Rheumatoid arthritis (RA) is a chronic, inflammatory, systemic autoimmune disease of unknown etiology. It is characterized by symmetric synovitis leading to cartilage damage and joint destruction and can be complicated by numerous extra-articular manifestations. Given the presence of autoantibodies, such as rheumatoid factor (RF) and anti-citrullinated protein antibody (ACPA), RA is considered an autoimmune disease. RA is generally a progressive disease with functional status decline, significant morbidity and premature mortality seen in established RA. The disease can occur at any age, with a peak incidence between the fourth and sixth decades. The goal of long-term RA treatment is disease remission.
Disease-modifying antirheumatic drugs (DMARDs), a heterogenous collection of agents grouped by use and convention, are the first line of treatment for RA patients. DMARDs are used to reduce joint swelling and pain, decrease acute-phase markers, limit the progression of joint damage and to improve joint function. DMARDs, most often methotrexate (MTX), are prescribed upon disease diagnosis (i.e., early RA), usually before the development of erosive disease and the deformities seen in established RA. MTX therapy is initiated if pain and synovitis persist (especially if function is compromised), and additional DMARDs (with or without steroids) may be added to achieve disease control. Unfortunately, only about ⅔ of patients respond to DMARDS, and DMARDs only partially control established RA disease. Radiological progression continues even in the 5-20% of DMARD-treated RA patients that achieve remission or clinical improvement that approaches remission. DMARDS also have many adverse effects (e.g., liver damage, bone marrow suppression and severe lung infection) that limit their prolonged use.
Due to the inadequate responses and dangers associated with prolonged DMARD treatment, biologics have been introduced as second line RA treatments. In general, anti-TNF agents (Cimzia®, Enbrel®, Humira®, Remicade®, Simponi®) are the first biologics used in DMARD-failure and DMARD-inadequate responder patients, and a TNF inhibitor is often combined with MTX (or another DMARD) to aggressively treat established RA. Unfortunately, 30-40% of patients with established RA fail to respond to TNF-α antagonists and the majority of those that respond initially do not achieve complete remission or lose response over time. Concerns have also been raised about the short and long-term tolerability and safety of chronic biologic treatment, most notably the reactivation of serious infections (e.g., tuberculosis infections), liver toxicity, increased cardiovascular disease, induction (or exacerbation of) demyelinating conditions, and increased incidence of malignancy due to TNF-alpha antagonism. M. Khraishi (2009) J. Rheumnatol Suppl. 82:25-32; Salliot et al. (2009) Ann. Rheum. Dis. 68:25-32. However, a TNF inhibitor is usually continued unless it becomes ineffective or an adverse event arises, at which point a clinician may switch to either a different TNF inhibitor or a biological with a different mechanism of action (e.g., Kineret® [IL-1R antagonist], MabThera® [CD20 antagonist], Orencia® [CTLA4 fusion protein] or Actemra® [IL-6 receptor antagonist]). Scott et al. (2010) The Lancet 376:1095-1108.
Given the aforementioned problems with current RA therapy, there is a need to develop new treatments for RA patients.